Police in Long Beach are warning residents about a possible crime spree this afternoon. It would be the latest in a string of so-called 'bash mobs' that recently struck Hollywood and San Bernardino. In each case, police arrested groups of teenagers accused of running through the streets and attacking and robbing local residents and tourists.

This would be the second crime wave in Long Beach this month. On July 9 more than 100 people descended on the streets of downtown in an organized, sudden crime rampage, police said.

What are these types of 'bash mobs'? How are police departments responding to these crime sprees? What can residents do to keep themselves safe?